In the past, it has been known that a polyurethane resin produced from a urethane prepolymer in which a silane compound having an amino group in a molecule is added to the terminal is excellent in physical properties such as elongation and toughness since the polyurethane resin has a urethane link and a urea link in a molecular chain (see, for example, Patent Documents 1 and 2). However, in the above-mentioned polyurethane resin, the prepolymer is alkaline due to a secondary amino group which remains in the prepolymer, and thereby a hydrolysis of an alkoxysilyl group proceeds. As a result, gelation occurs or viscosity increases and a problem such as poor storage stabilty arises.
As a process for eliminating an amino group which is alkaline, a process in which a silane compound having an amino group is added to an α-β-unsaturated carbonyl compound to form an alkoxysilane compound, and subsequently, the alkoxysilane compound is added to a urethane prepolymer is proposed (see, for example, Patent Document 3). However, when a polyurethane resin having low modulus and high elongation is produced by the above-mentioned process, the viscosity of the polyurethane resin increases and the handling property deteriorates. In addition, the production process is complex and expensive.    Patent Document 1: JP-A-03-047825    Patent Document 2: JP-A-03-157424    Patent Document 3: JP-A-2000-169544